Liebert 8 Tons User Manual

Steam generating humidifiers operate efficiently over a wide range of water quality conditions and 

automatically adjust to changes in the conductivity of water. The system will automatically drain and 

refill to maintain a current setpoint and alert the operator when the humidifier canister needs to be 

replaced. 
The humidifier RUN/DRAIN switch is located in the humidifier assembly. This switch should be in 

the RUN position when the humidifier is in normal operation, and in the DRAIN position during ser-

vice. The electronic control board for the humidifier is also located in the humidifier assembly. When 

the unit is energized, power is available to humidifier. Operation involves the following steps:
1. During start-up, when the humidity control calls for humidification, the fill valve will open, 

allowing water to enter the canister. When the water level reaches the electrodes, current flows 

and the water will begin to warm. The canister fills until the amperage reaches the setpoint and 

the fill valve closes. As the water warms, its conductivity increases and the current flow, in turn, 

rises. If the amperage reaches 115% of the normal operating amperage, the drain valve opens and 

flushes some of the water out of the canister. This reduces electrode contact with the water and 

lowers the current flow to the amperage setpoint. Boiling soon commences and the canister 

operates normally.

2. If the conductivity of the water is low, the canister fills and the water level reaches the canister 

full electrode before the amperage setpoint is reached. The humidifier stops filling to prevent 

overflow. Boiling should commence in time. As water is boiled off, the mineral concentration in 

the canister increases and current flow also increases. The canister eventually reaches full output 

and goes to normal operation. No drain is permitted until then.

3. When full output is reached the circuit board starts a time cycle which is factory set at 60 seconds. 

During this repeating time cycle, the fill valve will open periodically to replenish the water being 

boiled off and maintain a “steady state” output at the setpoint. The amperage variance will 

depend on the conductivity of the water.

4. After a period of time, the mineral concentration in the canister becomes too high. When this 

occurs, the water boils too quickly. As the water quickly boils off and less of the electrode is 

exposed, the current flow decreases. When the current crosses the low threshold point (factory set 

at 85%) before the end of the time cycle, the drain valve opens, draining the mineral laden water 

out and replacing it with fresh water. This lowers the mineral concentration and returns the 

canister to “steady state” operation and prolongs canister life. The frequency of drains depends on 

water conductivity.

5. Over a period of time, the electrode surface will become coated with a layer of insulating material, 

which causes a drop in current flow. As this happens, the water level in the canister will slowly 

rise exposing new electrode surface to the water to maintain normal output. Eventually, the 

steady state water level will reach the canister full electrode and indicate so by activating the 

canister full alarm. At this point, all of electrode surface has been used up and the canister should 

be replaced.

6. After the entire electrode surface has been coated, the output will slowly decrease. During these 

last hours of electrode life, the mineral concentration can increase and arcing can occur. If the 

electrodes start to arc, turn off the humidifier immediately and replace the canister with the 

identical part.